The White House on Tuesday reiterated opposition to any new sanctions against Iran related to the country's nuclear program, even conditional sanctions that wouldn't take effect for six months.

It's a move that could put the kibosh on an attempt by top Senate Democrats to push new restrictions on the country.

"We strongly believe that passing new sanctions now will result in our international partners, as well as Iran, seeing us as having negotiated that agreement in bad faith, which would then have a bearing on our core sanctions architecture," White House Press Secretary Jay Carney said. "The sanctions regime that [Congress] helped us build has provided this opportunity. It has succeeded in the sense that the sanctions were designed to pressure Tehran into changing its behavior, and because of the impact of the sanctions, Tehran has changed its behavior — or indicated that it is willing to change its behavior."

Carney declined to specifically issue a blanket veto threat, noting there was no Statement of Administration Policy to announce.

That's no surprise, because there's no legislation yet. However, Foreign Relations Chairman Robert Menendez, D-N.J., and like-minded senators in both parties appear to be coalescing around an additional sanctions regime that would take effect in six months if subsequent conversations between the P5+1 countries and Iran fail to yield results.

On the Democratic side, the group favoring that idea includes No. 3. Democrat Charles E. Schumer of New York, though Senate Majority Leader Harry Reid, D-Nev., has been noticeably more circumspect.

"I hope the negotiations succeed. They're important. I worry that what we’re giving is not proportional to what we're getting. I worry about a diminution of sanctions. It's sanctions that brought the Iranians to the table," Schumer said in an interview with the New Republic, according to an edited transcript. "They are effective by all accounts. Part of sanctions is the actual economic bite that occurs. But another part is the psychological fear that they will get worse."

"It seems to me that prospectively looking for sanctions that are invoked six months from the date of enactment — they give the president certain waivers — therefore creates the flexibility for diplomacy, also sends a message to Iran, as it has throughout this process, that there is a consequence if you don't strike a successful deal and puts us in a position of having the insurance to have additional sanctions go into effect at that time, and at the same time gives the administration the flexibility to negotiate," Menendez said on CBS. "So I think that's a very responsible position."

But the Obama administration clearly wants the Senate to stand down from any new legislative effort.

"Our belief is that if sanctions were passed now, even with a delayed trigger, that it would undermine the core sanctions regime and would potentially undermine the negotiations," Carney said. "If you want to resolve this peacefully, we need to test whether or not Tehran is willing to do what it takes, and to make the — commitments necessary to resolve this peacefully, and the only way we can do that."

"We believe that Congress should hold in reserve ... the option of passing new sanctions if the moment arises when Iran has failed to comply with its agreement, and that taking that action would have a positive result," Carney said.

Appearing on CBS with Menendez, Foreign Relations ranking member Bob Corker said he didn't expect the Iranian government to make any provocative moves in the immediate future.

"I think they're going to be good actors over the next six months. Because they see an administration who led this negotiation, an administration that has already given tilt to allowing them to do the things that the world community, through the U.N. Security Council, has already said they cannot do. So I'm very discouraged," the Tennessee Republican said.